Mechanical Behaviour of Rubber Material with Consideration to Mullins Effect

A stress softening known as the Mullins effect is observed usually in rubberlike material after the first load. This paper describes an experimental test method for defining the nonlinear properties of rubber materials used for finite element analysis. Experimental observations have shown that the Mullins effect induces a permanent set and some anisotropy. To test the Mullins effect the mechanical preconditioning is suggested to stabilize the properties of rubber material. A stress-strain curve will change significantly when the rubber material is strained greater than the previous stabilized level. Therefore, material properties at maximum strain level are obtained to predict behavior of rubber products. To obtain the rubber material constants used for finite element analysis to understand the characteristics of automotive rubber parts, mechanical properties tests such as uniaxial tension, equ-biaxial tension and pure shear tests are required. When the load was repeatedly applied to the rubber specimen, the stress-strain relationship was greatest in the first and second cycles, and the larger the strain range, the more the stress was reduced. The material constants were obtained using the stress-strain data after the rubber specimen was stabilized. The value of stiffness decreased as the maximum strain range increased. The static stiffness of an automotive engine mount is calculated by nonlinear finite element analysis using the experimentally determined material constants and compared with the experimental results considering the mechanical preconditioning effect resulting in a good correlation.

Moment Measurements in Dynamic and Quasi-Static Spine Segment Testing Using Eccentric Compression are Susceptible to Artifacts Based on Loading Configuration

The tolerance of the spine to bending moments, used for evaluation of injury prevention devices, is often determined through eccentric axial compression experiments using segments of the cadaver spine. Preliminary experiments in our laboratory demonstrated that eccentric axial compression resulted in “unexpected” (artifact) moments. The aim of this study was to evaluate the static and dynamic effects of test configuration on bending moments during eccentric axial compression typical in cadaver spine segment testing. Specific objectives were to create dynamic equilibrium equations for the loads measured inferior to the specimen, experimentally verify these equations, and compare moment responses from various test configurations using synthetic (rubber) and human cadaver specimens. The equilibrium equations were verified by performing quasi-static (5 mm/s) and dynamic experiments (0.4 m/s) on a rubber specimen and comparing calculated shear forces and bending moments to those measured using a six-axis load cell. Moment responses were compared for hinge joint, linear slider and hinge joint, and roller joint configurations tested at quasi-static and dynamic rates. Calculated shear force and bending moment curves had similar shapes to those measured. Calculated values in the first local minima differed from those measured by 3% and 15%, respectively, in the dynamic test, and these occurred within 1.5 ms of those measured. In the rubber specimen experiments, for the hinge joint (translation constrained), quasi-static and dynamic posterior eccentric compression resulted in flexion (unexpected) moments. For the slider and hinge joints and the roller joints (translation unconstrained), extension (“expected”) moments were measured quasi-statically and initial flexion (unexpected) moments were measured dynamically. In the cadaver experiments with roller joints, anterior and posterior eccentricities resulted in extension moments, which were unexpected and expected, for those configurations, respectively. The unexpected moments were due to the inertia of the superior mounting structures. This study has shown that eccentric axial compression produces unexpected moments due to translation constraints at all loading rates and due to the inertia of the superior mounting structures in dynamic experiments. It may be incorrect to assume that bending moments are equal to the product of compression force and eccentricity, particularly where the test configuration involves translational constraints and where the experiments are dynamic. In order to reduce inertial moment artifacts, the mass, and moment of inertia of any loading jig structures that rotate with the specimen should be minimized. Also, the distance between these structures and the load cell should be reduced.

Experimental Investigation on Damping Characteristic of Metal Rubber Material at Simulated Marine Environment

To meet the need of damping material at the marine corrosive environment, the clamped-edge disk type of metal rubber specimen is designed and its corrosion-load alternate experiment is performed, the anti-corrosive and damping characteristic of the material at the marine corrosive environment is researched. The experimental results show that the corrosive rate of 304 stainless steel metal rubber specimen at cycle-immersion corrosion-load alternate environment is the highest and its decay rate of dynamic average rigidity is also the highest, and followed by full-immersion, cycle-salt-spray and full-salt-spray environment. The damping characteristic of metal rubber specimen is relatively stable at the corrosion-load alternate experiment; the metal rubber material has anti-corrosion ability at marine environment.

Friction Characteristics of Porous Rubber Under Wet Conditions

In recent years, porous rubber has been used as a tread matrix for studless tires. It is said that the pores in the tread rubber remove water between the tire and the wet road surface; however, the water removal is not sufficiently well understood. In this study, a rotating rubber specimen was rubbed against a mating prism to observe the contact surface. The friction force was also measured simultaneously with observation of contact surface. The water entering the pores was distinguished by the continuity method. As the result of these experiments, the coefficient of friction for rubber having pores on the surface was found to be larger than that of rubber without pores. Moreover, the difference in the coefficient of friction for rubber specimens with and without pores tended to be larger at lower sliding speeds. No water entered pores 3mm or less in diameter at any sliding speed in this experiment. An experiment to make the rubber specimen collide with the mating prism was conducted since actual tires seem to be deformed by the vehicle weight, such that the tire surface might contact the road collisionally. In the resulting collision experiment, the water did enter pores 3mm in diameter.

Deformation Behavior of Metal Rubber Material

Analysed the stress-strain test in the pressing direction of metal rubber specimen, the deformation process can be divided into three stages. Used the accumulative method of high step polynomial, the experience formula of metal rubber’s deformation character can be simply and effectively established. With the fabrication and formation technology, the microscopic physics mechanism has been analyzed in these deformation stages.